Laboratory Testing in a 98-Year-Old Nursing Home Resident
Laboratory testing should only be performed when there is clinical suspicion of infection or acute illness, not as routine screening. 1, 2
When to Order Labs
Perform laboratory testing if the resident has:
Suspected infection based on fever (single oral temp ≥100°F or repeated temps ≥99°F) or functional decline (new confusion, incontinence, falls, reduced mobility, decreased food intake, or failure to cooperate with staff) 1
Acute clinical deterioration requiring diagnostic evaluation to guide management 1
Do NOT order labs if:
- The resident is asymptomatic and clinically stable 1, 2
- Results will not change your management strategy 1
- Advance directives limit diagnostic interventions 1, 2
Critical Caveat: Advance Directives First
Always review advance directives before ordering any laboratory tests. 1, 2 If directives limit interventions or the resident has poor survival prognosis, withholding diagnostic studies is appropriate unless there is risk to other residents or staff. 1 Document your reasoning if tests are consciously withheld. 1
What Labs to Order When Infection is Suspected
Within 12-24 hours of symptom onset (sooner if seriously ill): 1, 2
- Complete blood count (CBC) with manual differential to assess bands and immature forms 1, 2
- WBC ≥14,000 cells/mm³ has likelihood ratio of 3.7 for bacterial infection 1, 2
- Left shift (band neutrophils ≥16% or total band count ≥1,500 cells/mm³) has likelihood ratio of 14.5 for bacterial infection 1, 2, 3
- Leukocytosis is associated with increased mortality in nursing home-acquired pneumonia and bloodstream infections 1
For suspected urinary tract infection (UTI):
- Do NOT order urinalysis or urine culture if asymptomatic 1
- Only order if acute UTI symptoms present: fever, dysuria, gross hematuria, new/worsening incontinence, or suspected bacteremia 1, 2
- Start with urinalysis (dipstick for leukocyte esterase/nitrite, microscopy for WBCs) 1
- Order urine culture only if pyuria present (≥10 WBCs/high-power field or positive dipstick) 1
For suspected urosepsis (fever, shaking chills, hypotension, delirium):
- Obtain paired blood and urine cultures with Gram stain of uncentrifuged urine 1
- Change indwelling catheter before specimen collection 1
When Labs Are NOT Indicated
In the absence of fever, leukocytosis, left shift, or specific focal infection signs, additional diagnostic tests have low yield and are not indicated. 1, 2 However, nonbacterial infections cannot be excluded. 1
Cost-Effectiveness Considerations
Tests should only be performed if they have: 1, 2
- Reasonable diagnostic yield
- Low risk to the patient
- Reasonable cost
- Potential to improve patient management
If a test won't change your treatment strategy, don't order it. 1, 2
Common Pitfalls to Avoid
Don't order routine annual screening labs - only 16.7% of annual panels in skilled nursing facilities resulted in patient benefit, and most could have been detected through monitoring of known chronic conditions 4
Don't rely solely on fever - typical infection symptoms are frequently absent in frail elderly, and basal body temperature decreases with age 1, 2
Don't ignore functional decline - new confusion, falls, or reduced food intake may be the only sign of serious infection 1
Don't order tests that won't change management - this is especially relevant given the Prospective Payment System constraints in nursing homes 1
Age-Specific Laboratory Considerations
At 98 years old, recognize that: 5
- Serum creatinine may appear normal despite markedly decreased creatinine clearance
- ESR up to 40 mm/hr may be acceptable
- Hemoglobin as low as 11.0 g/dL (women) or 11.5 g/dL (men) may be acceptable
- BUN up to 28-35 mg/dL may be normal
These physiologic changes mean laboratory values must be interpreted in clinical context, not in isolation. 5, 6